1. Field of the Invention
The present invention relates to a storage device and a control method thereof, and more particularly to a storage device which is preferably used as a storage device provided with an external connection function.
2. Description of the Related Art
Conventionally, as one of functions of the storage device, there has been known an external connection function which virtualizes a logical volume which other storage device connected to an own storage device (hereinafter referred to as an external storage device) provides (see JP-A-2006-331458).
In the storage device to which the external connection function is imparted (hereinafter referred to as “main storage device”), virtual logical volumes are set in the virtualized external storage device in a state that the virtual logical volumes are respectively made to correspond to logical volumes.
Further, the main storage device, when a read request or a write request is given to a certain virtual volume from a host computer, issues a command corresponding to the read request or the write request to the external storage device having the corresponding logical volume, and allows the external storage device to execute actual read processing or write processing.
According to such an external connection function, it is possible to realize the unity of management of the logical volumes which a plurality of external storage devices provides respectively and hence, the storage device has an advantageous effect that the addition of a storage device or the like can be easily realized.
Here, JP-A-2006-331458 discloses a technique in which when the main storage device transmits a command corresponding to a read request or a write request from a host computer to the corresponding external storage device, a processing state of read processing or write processing in the external storage device is monitored, and load distribution processing is executed when necessary.